LIGHT-INDUCED CHLOROPLAST ALPHA-AMYLASE IN PEARL-MILLET (PENNISETUM-AMERICANUM)

In pearl millet (Pennisetum americanum) seedlings light induces the appearance of a leaf alpha-amylase isozyme. The leaf alpha-amylase isozyme was present in enriched amounts in isolated chloroplasts but it could not be detected in isolated etioplasts. The chloroplast alpha-amylase was present in both mesophyll and bundle-sheath chloroplasts. Preliminary characterization indicated that molecular properties of chloroplast alpha-amylase were like those of a typical alpha-amylase. The plastidic alpha-amylase had a molecular mass of 46 kD, pH optimum of 6.2, required Ca2+ for activity and thermostability, but lost activity in the presence of ethylenediaminetetracetate. Plastidic alpha-amylase activity after sodium dodecyl sulfate-polyacrylamide gel electrophoresis could be renatured in situ by Triton X-100. Western blot analysis demonstrated that this protein was antigenically similar to a maize seed alpha-amylase. In vivo [S-35]methionine labeling of bundle-sheath strands isolated from light-grown leaves followed by immunoprecipitation revealed that bundle-sheath strands synthesized plastidic alpha-amylase de novo.